In a communication system, when a bit stream is sent from a transmitter to a receiver, this receiver is often synchronized with the transmitter in order to be able to reconstruct the structure of the received bit stream in a simple and efficient way. Sometimes, it may happen that this synchronization between receiver and transmitter is lost. So, there are methods to resynchronize the receiver with the transmitter.
According to a first prior art, it is known a first type of resynchronization process where both transmitter and receiver cooperate by exchanging messages in order to resynchronize the receiver with the transmitter. If an error is detected at the receiver, a resynchronization process is started, which could last relatively long. Indeed several steps are performed. First a packet is built on the receiver side. Then, this packet is transmitted to the transceiver. Afterwards, the transceiver starts a Synchronization Sequence, which is an easy and predefined sequence of bits, to allow the desynchronized receiver to resynchronize itself with the transmitter. Therefore, the receiver must re-extract the boundaries between groups of bits. To do so, typically, it sequentially probes all the possible boundaries, which means all the N possible boundaries, if the groups of bits each contain N bits. One drawback of this first prior art is that the duration of the sequence is relatively long.
According to a second prior art, it is known a second type of resynchronization process where the receiver alone tries to find back the boundaries between groups of bits to be able to resynchronize by itself with the transmitter. To do so, the receiver chooses a group of a length of N bits, if groups are supposed each to contain N bits. The receiver looks at this N bits group to check if this N bits group is consistent. This test can have two outcomes: either it is consistent or it is not. If this N bits group is consistent, then the receiver has found the good N bits group boundary and the receiver is resynchronized with the transmitter. If this N bits group is not consistent, then the receiver shifts the group of N bits of 1 bit, and retries to see if this new group of N bits is consistent. The receiver iterates this shifting and testing couple of operations until the receiver finds a good group, in a chronological reception of order from the first bit used to start the process. One drawback of this second prior art is that this process is still fairly long. Indeed, the first bit of a group of N bits can be anywhere among the N bits of a group. At best, the good bit is found immediately. At worst, it is found after N iterations. In the average, it is found after N/2 iterations. The N/2 average iterations mean usually about N2/2 bits lost before the synchronization of the receiver with respect to the transmitter is re-acquired. It will be seen later, that even if the starting bit for the process has been chosen as the most probable first bit, it still remains fairly long.